For an object produced during the medieval period, this astrolabe is unusually well documented. Its inscription attributes it to a Rasulid prince, 'Umar ibn Yusuf, a few years before he ascended to the throne (r. 1295–96). 'Umar compiled a number of scientific treatises, including one on the construction of astrolabes, an autographed version of which, preserved in Cairo, contains certifications by his teachers as to his competence as a maker of such devices and a description of this very piece.

Invented in antiquity and refined in various regions of the Islamic world during the medieval period, the astrolabe was used to locate the qibla direction, establish correct prayer times, predict positions of heavenly bodies, and determine horoscopes, among other purposes.[2] The present piece is an extraordinarily well-documented example. Its inscription attributes it to a Rasulid prince of Yemen, ‘Umar ibn Yusuf, and dates it a few years before ‘Umar ascended to the throne under the regnal name al-Ashraf (1295–96). ‘Umar is known to have compiled a number of treatises on subjects related to the sciences, including a text on the construction of astrolabes, sundials, and magnetic compasses.[3] One of the extant manuscripts of this treatise (possibly an autograph version) contains not only illustrations and tables that correspond to this astrolabe but also a certification by ‘Umar’s teachers attesting to his competence as a maker of such devices and describing several of his works, one of which can be identified with this very piece.[4] On the basis of that description and the particular wording at the end of the inscription, it has been proposed that the astrolabe was created by the prince in collaboration with an unnamed metalworker.[5]In most respects, ‘Umar’s instrument follows the form typical of other astrolabes from the medieval Islamic world. Made of brass, it consists of a rotating rule; an openwork rete, or "star-net," with an ecliptic ring and star pointers; a case, or mater, housing four plates; a rotating sighting bar, or alidade, on the back of the case; and a pin (modern). The back of the case bears the previously mentioned inscription along with several registers of astrological symbols and notations. From the top there protrudes a decoratively pierced suspension bracket of arabesque design attached to two rings. Inscribed around the outer edge of the rete are the names of the twenty-eight lunar mansions. One of the four plates is not original and appears to have been reused from another astrolabe. The others, all original, bear the latitudes for four specific locations in Yemen as well as for Mecca and Medina.[6]Ellen Kenney in [Ekhtiar, Soucek, Canby, and Haidar 2011]Footnotes:2. An explanation of astrolabes and their uses is found in Maddison, Francis, and Emilie Savage-Smith. Science, Tools and Magic. Pt. 1, Body and Spirit, Mapping the Universe. The Nasser D. Khalili Collection of Islamic Art, edited by Julian Raby, vol. 12. [London], 1997, pp. 168–282.3. Copies of this text survive in Cairo, Tehran, and Berlin (nos. TR 105, MUI 150, and Ahlwardt 5811 [Sprenger 1870], respectively). On the particular interest in astronomy demonstrated in Yemen, see King, David A. Mathematical Astronomy in Medieval Yemen: A Biobibliographical Survey. Catalogs (American Research Center in Egypt), 4. Malibu, 1983.4. Cairo TR 105. These evaluations are based on ‘Umar’s completion of six astrolabes and two magnetic compasses, as well as other instruments (King, David A. "The Medieval Yemeni Astrolabe in the Metropolitan Museum of Art in New York City." Zeitschrift für Geschichte der arabisch-islamischen Wissenschaften 2 (1985), p. 101; 4 (1987–88), pp. 268–69 [errata].5. The Museum’s astrolabe is the only instrument that has been securely attributed to this ruler.6. Aden, Ta‘izz, Sana‘a, and North Yemen (King 1985 [see footnote 4], p. 104).

Signatures, Inscriptions, and Markings

Signature: Made and signed by the Rasulid prince al-Ashraf `Umar ibn Yusuf, later Sultan of Yemen (r.1295-96).